I once knew a website where the user could generate the little W3C valid CSS tags which looked much nicer than the too large W3C official ones. It was also possible to fill the icons with whatever content and color for other stuff.
I've lost the bookmark and wasn't able to google it, can you post it and maybe other such resources?
EDIT: and yes I know ...
Can I modify the existing icons to create my own?
No. The validator's icons are distributed under the W3C document license, which allows distribution but does not allow derivative works.
BUT I don't care, cause I don't want my design to look ugly.